Re: [PATCH 08/17] x86/ftrace: set trampoline pages as executable

On Wed, 6 Feb 2019 09:33:35 -0800
Nadav Amit [off-list ref] wrote:

quoted

quoted

	/* Copy ftrace_caller onto the trampoline memory */
	ret = probe_kernel_read(trampoline, (void *)start_offset, size);

@@ -818,6 +820,13 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)

	/* ALLOC_TRAMP flags lets us know we created it */
	ops->flags |= FTRACE_OPS_FL_ALLOC_TRAMP;

+	/*
+	 * Module allocation needs to be completed by making the page
+	 * executable. The page is still writable, which is a security hazard,
+	 * but anyhow ftrace breaks W^X completely.
+	 */  

Perhaps we should set the page to non writable after the page is
updated? And set it to writable only when we need to update it.  

You remember that I sent you a patch that changed all these writes into
text_poke() and you said that I should defer it until this series is merged?

And I notice that it is set to RO after this call anyway.

-- Steve